The present invention relates to a method and device for controlling a pump of a brake system, such as in an anti-skid control system, a friction control system, or a vehicle dynamics control system.
German Patent Application 42 32 130 describes a method and a device for controlling an electric motor-driven hydraulic pump that is used to generate the servo pressure of a brake system with anti-skid control and/or traction control. For this purpose, it is driven with a variable drive cycle composed of a pulse/pause sequence. The voltage regeneratively induced by the pump motor in the interpulse pauses is evaluated as a measure of pump speed. The computed difference between this generator voltage as an actual speed quantity and a setpoint quantity for the pump motor speed formed in an anti-skid control or traction control system provides a differential quantity to a downstream controller. The pulse width-modulated actuating signal for driving the pump is formed with the output signal from the controller. The drive motor of the hydraulic pump is turned on and off with the clock pulse of this pulse width-modulated actuating signal.
The conventional method and corresponding device are unable to provide optimum results in every respect. An object of the present invention is to provide an optimized method that can also offer the driver a comfortable pedal sensation independently of the setpoint quantity formation, at the same time providing a simple control structure.
German Patent Application No. 198 18 174 (not a prior-publication) describes a method for controlling a pump of a brake system, in which a pump is initially connected to the voltage supply for a specifiable period of time, in response to a pumping request in a brake system. Subsequently, the pump then receives at least one control signal, which is constant for at least one time interval and is formed from the sum of the pulse duration and interpulse period. In this drive cycle, a drive pulse for switching the pump on again is generated based on a comparison of a motor voltage to threshold voltage values. Consequently, the starting pulse for the pump is not generated until a load occurs, which is characterized by the motor voltage reaching a threshold voltage value. Preventive recognition of a load situation and intensified driving of the pump resulting from this, are not shown. In addition, this patent only starts with an arbitrary control algorithm or a feedback control. The use and coordination of several simultaneously active feedback controls acting on the pump is not shown.
Initially, according to an example embodiment of the present invention, the pump is not clocked and is driven at full load for a selected time TAnstMax, i.e., full supply voltage Ubat, in particular, is applied to the pump, driving the latter with a clocked PWM signal that is derived from a direct comparison between motor voltage UM, which drops across the pump motor, and at least one selected voltage threshold value Us. For safety reasons, a minimum on-time TPeinMin=TTaktxe2x88x92TPausMax of the pump can be maintained within a drive cycle by a predetermined maximum off-time TPausMax. Also due to safety considerations, the pump is driven at full load upon reaching a minimum voltage threshold Uss, i.e., supply voltage Ubat, in particular, is applied to the pump motor for a certain period of time. By using motor voltage UM in a direct comparison with different voltage threshold values, the method can be used independently of the controller concept.
The method and device according to the present invention, comma have the advantage that not only is the equipment and methodological design simple, but they can be used independently of the brake logic (e.g., anti-skid control/traction control/vehicle dynamics control system). In addition, the forced pumping action of the pump during drive cycle period TTakt produces a defined pedal sensation. This continuous availability of the active pressure variation in the brake circuit, due to minimum pump on-time TPeinMin, is also secondarily relevant to safety. Defined minimum pump on-time TPeinMin per clock cycle TTakt avoids what may be a large difference between the existing pressure and the pressure needed in the brake circuit, e.g., when a sudden pumping request is received from the brake system. This makes it possible to maintain a low average speed of the pump motor, since the pump is additionally fully driven when subjected to a heavy load, and consequently upon meeting certain conditions, in particular when motor voltage UM reaches a selectable safety threshold voltage Uss. Using a variable number of threshold values and different clock cycle times and/or driving times assigned to them makes it possible to adapt the system to any braking situation. The variable pump on- and off-times advantageously make it possible to reduce the pump motor speed without sacrificing performance.
It is also advantageous for the pump motor voltage to drop to a value that is less than a further threshold voltage during normal clocking operation, in which case this further threshold value can also correspond to safety threshold Uss or another threshold voltage Us, thus reactivating the pump for the rest of the cycle, additionally increasing availability.
If pump motor voltage UM drops to a value that is smaller than, for example, safety threshold value Uss directly after the pump is turned off, i.e., during the next cycle, the pump is reactivated for a selectable period of time. By allowing pump motor voltage UM to drop immediately after deactivation reveals that the pump is under heavy load during this phase. Consequently, the pump can be driven during this phase for a time that is much longer than the drive cycle period. This critical threshold, e.g., Uss, can be used to simultaneously prevent the pump motor from remaining at a standstill.
According to one advantageous embodiment, the method for driving the pump motor is designed so that the pump driving action according to one control strategy, e.g., traction control, is independent of the pump driving action according to another control strategy, such as anti-skid control. This can be accomplished by using different parameters and different logic components for the control systems. Each control strategy, i.e., each control systemxe2x80x94such as anti-skid control or traction controlxe2x80x94can intervene in pump motor clocking at any time, depending on certain input, e.g., using a flag. A priority control system can also avoid additional pump driving conflicts. This enables intervention to be made in the pump motor clocking at any time so that the pump is switched between continuous and full drive. This makes it possible to provide a modular pump motor drive mechanism that uses only one algorithm or only one basic logic. In this module, independent pump motor clocking of the individual systems i.e., control arrangements influencing the braking action can be operated simultaneously to ensure vehicle driving stability and/or safety.
Further advantages lie in reducing the pump motor current and consequently in dimensioning the pump motor, since it needs to be driven continuously only for a short period of time. The duration of full drive can be limited by estimated wheel break pressures, especially when decreasing from a high wheel pressure level.
A pump motor module can also be provided with an additional input for a flag. Controlled, for example, by the traction control algorithm, this flag can be used to immediately disable clocking of the pump driving action, e.g., by the anti-skid control system, and the pump can be driven in a different mode. The same also applies, of course, to all systems, i.e., control arrangements influencing the braking action to provide vehicle driving stability and/or safety.
With the embodiments described above and the conditions selected therein, the pump can be driven selectively and optimized to its requirements and the current operating mode.